1. Field of the Invention
The present invention relates to a stereoscopic image display apparatus permitting observation of a stereoscopic image without a need for special glasses and, more particularly, to the apparatus suitably applicable to stereoscopic display in a television, a video system, a computer monitor, a game machine, and so on, which is arranged in such structure that a predetermined emission pattern is formed by a self-emission type display element such as a CRT or the like or light from an illumination light source is made to pass through aperture portions of a mask pattern having the aperture portions and shield portions arrayed at a predetermined pitch to pattern the passing beam, directivity is given to the patterned beam by an optical system having so patterned fine structure as to make the patterned beam incident separately to the right eye and to the left eye of an observer, a transmission type display device is disposed between the patterned optical system and the observer, and the display device is arranged to display a stripe image synthesized in alternate stripes of parallax images corresponding to the right eye and to the left eye, so as to permit the observer to observe a stereoscopic image.
2. Related Background Art
Applicant of the present application suggested in Japanese Laid-open Patent Application No. 9-311294 the stereoscopic image display apparatus constructed in such structure that the predetermined emission pattern is formed by the self-emission type display element such as the CRT or the like or the light from the illumination light source is made to pass through the aperture portions of the mask pattern having the aperture portions and shield portions arrayed at the predetermined pitch to pattern the passing beam, directivity is given to the patterned beam by the optical system having so patterned fine structure as to make the patterned beam incident separately to the right eye and to the left eye of the observer, the transmission type display device is disposed between the patterned optical system and the observer, and the display device is arranged to display the stripe image synthesized in alternate stripes of the parallax images corresponding to the right eye and to the left eye. FIG. 5 is a perspective view for explaining the fundamental structure of the stereoscopic image display apparatus disclosed in the above application.
In FIG. 5 reference numeral 1 schematically illustrates a liquid crystal display (LCD) for display of a image. Numeral 5 represents a back light as an illumination light source. Disposed in front of the back light 5 is a mask substrate 4 on which a mask pattern 7 having apertures 6 of a checkered pattern to transmit light is formed. Provided between the mask substrate 4 and LCD 1 are two lenticular lenses 2, 3 (a vertical lenticular lens 3 and a horizontal lenticular lens 2) which are made of transparent resin or glass in the form of microlenses and which are arranged perpendicular to each other. As illustrated, the left and right parallax images L, R are displayed in an array of horizontal stripes alternated in the vertical (altitudinal) direction in the LCD 1.
The light from the back light 5 passes through each aperture 6 of the mask substrate 4 and illuminates the LCD 1 through the vertical and horizontal lenticular lenses 3, 2, so that the left and right parallax images are separated to both eyes of the observer to be observed thereby.
According to the embodiment disclosed in the above application, pixels on the LCD 1 are illuminated by beams with intensities varying at a pitch Hi nearly equal to a horizontal pitch HL of the vertical cylindrical lenses of the vertical lenticular lens 3 in the horizontal direction.
In this structure moire fringes will appear in a vertical stripe pattern periodically to change the brightness of the LCD screen in the horizontal direction if the difference between the horizontal pitch Hi of the illumination light and the horizontal pixel pitch Hd of the pixels of the LCD 1 is within a certain range. Those moire fringes will impede the observation of stereoscopic image.
For the sake of simplicity, the horizontal distribution of intensities of the illumination light and the transmittance distribution of the LCD due to the aperture portions and the shield portions of black stripes or the like are expressed respectively as follows by cosine functions. EQU I.multidot.cos [(2.pi./Hi).multidot.x], T.multidot.cos [(2.pi./Hd).multidot.x]
Here, I indicates the amplitude of change of illumination intensities, T the amplitude of change of LCD transmittances, and x coordinates in the horizontal direction.
The distribution of illumination light immediately after transmission through the LCD, I-LCD, is expressed in the form of the product of the above two functions and is modified as follows by use of the cosine product formula. EQU I-LCD=R.multidot.cos [(2.pi./Hi).multidot.x].multidot.T.multidot.cos [(2.pi./Hd).multidot.x]={cos [2.pi..multidot.(1/Hi+1/Hd).multidot.x]+cos [2.pi..multidot.(1/Hd-1/Hi).multidot.x]}.multidot.I.multidot.T/2
The first term is a term varying at the pitch, 1/(1/Hi+1/Hd)=Hi.multidot.Hd/(Hi+Hd)&lt;Hi, Hd. Since this pitch is much smaller than the horizontal pixel pitch Hd of the LCD 1, the observer cannot visually recognize it.
The second term is a term varying at the pitch, 1/(1/Hd-1/Hi)=Hi.multidot.Hd/(Hi-Hd). This pitch becomes large enough for the observer to visually recognize it where the horizontal pitch Hi of the illumination light is close to some extent to the horizontal pixel pitch Hd of the LCD pixels. The second term is a term appearing as vertical stripes on the LCD screen.
In practice, the horizontal distribution of the illumination light and the horizontal transmittance distribution of the LCD are not of the simple cosine function forms but much more complicated periodic distributions. However, where each distribution is expressed in the form of a Fourier integral, the cosine function described above is a main component in each Fourier integral and thus the moire fringes appearing have the main pitch represented by the pitch described above.